Problem: 3 rubber stamps cost $5.91. Which equation would help determine the cost of 14 rubber stamps?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 3 rubber stamps. We want to know the cost of 14 rubber stamps. We can write the numbers of rubber stamps as a proportion: $\dfrac{3}{14}$ We know 3 rubber stamps costs $5.91. We can let $x$ represent the unknown cost of 14 rubber stamps. The proportion of these costs can be expressed as: $\dfrac{\$5.91}{x}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{3}{14} = \dfrac{\$5.91}{x}$